Some muster drills are too long. On one cruise we had to stand outside in the hot sun for about an hour because some passengers hadn't shown up. My poor old Mum nearly passed out; we had to find somewhere for her to sit and then find some water for her.
On our world cruise last year we had lots of muster drills, inside with seating, which wasn't too bad. I got tired of them playing the Love Boat theme though.